Influence of comfort and social stimuli on a comfort movement and a display derived from it
We tested the extent of emancipation of the Whistle-shake display of male shelducks, Tadorna tadorna, from causal factors controlling its presumed evolutionary precursor, the Body-shake, a comfort movement. Both motor patterns show similarities in form and alternate in a yearly rhythm. First, in an artificial rain experiment, we analysed the influence of a stimulus controlling comfort movements. In spring almost exclusively Whistle-shakes were induced even in the absence of social stimuli, while in summer the birds performed predominantly Body-shakes. This is probably related to the seasonal production of sex hormones. Second, we tested the influence of social stimuli by confronting shelducks with displaying and non-displaying males. During moult when males almost exclusively perform Body-shakes we found no influence of social stimulation on the frequency or form of shakes. However, an effect of social stimulation was found in a period when the drakes gradually replace the Body-shake by the Whistle-shake which is after moult in autumn. In this experiment, birds were confronted with either an empty cage (control), artificial rain, a non-displaying or a displaying male conspecific. In relation to the control situation the birds performed more Whistle-shakes when stimulated socially and more Body-shakes when stimulated with artificial rain. The extent to which both shaking patterns share the same causal factors is discussed. Copyright 1998 The Association for the Study of Animal Behaviour.
Sebbel
P
Department of Behavioural Biology, University of Groningen
D&Uuml;TTMANN
H
Groothuis
T